Anode material having a uniform metal-semiconductor alloy layer

ABSTRACT

The present invention relates to methods for producing anode materials for use in nonaqueous electrolyte secondary batteries. In the present invention, a metal-semiconductor alloy layer is formed on an anode material by contacting a portion of the anode material with a solution containing metals ions and a dissolution component. When the anode material is contacted with the solution, the dissolution component dissolves a part of the semiconductor material in the anode material and deposit the metal on the anode material. After deposition, the anode material and metal are annealed to form a uniform metal-semiconductor alloy layer. The anode material of the present invention can be in a monolithic form or a particle form. When the anode material is in a particle form, the particulate anode material can be further shaped and sintered to agglomerate the particulate anode material.

This application is a continuation-in-part of U.S. application Ser. No.12/105,090, filed Apr. 17, 2008. This application also claims thebenefit of U.S. Provisional Application No. 61/045,886, filed Apr. 17,2008. The contents of the above two identified applications areincorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to anode materials having a uniformmetal-semiconductor alloy layer and methods for making such anodematerials. The anode material is useful for nonaqueous electrolytesecondary batteries.

BACKGROUND OF THE INVENTION

Nonaqueous electrolyte secondary batteries are a type of rechargeablebattery in which ions move between the anode and cathode through anonaqueous electrolyte. Nonaqueous electrolyte secondary batteriesinclude lithium-ion, sodium-ion, and potassium-ion batters as well asother battery types.

Lithium-ion batteries are a popular type of nonaqueous electrolytesecondary battery in which lithium ions move between the cathode and theanode thought the electrolyte. The benefits and the challenges oflithium-ion batteries are exemplary of the benefits and challenges ofother nonaqueous electrolyte secondary batteries; the following examplespertaining to lithium-ion batteries are illustrative and are notlimiting. In lithium-ion batteries, the lithium ions move from the anodeto the cathode during discharge and from the cathode to the anode whencharging. Lithium-ion batteries are highly desirable energy sources dueto their high energy density, high power, and long shelf life.Lithium-ion batteries are commonly used in consumer electronics and arecurrently one of the most popular types of battery for portableelectronics because they have high energy-to-weight ratios, no memoryeffect, and a slow loss of charge when not in use. Lithium-ion batteriesare growing in popularity for in a wide range of applications includingautomotive, military, and aerospace applications because of theseadvantages.

FIG. 1 is a cross section of a prior art lithium-ion battery. Thebattery 15 has a cathode current collector 10 on top of which a cathode11 is assembled. The cathode current collector 10 is covered by aseparator 12 over which an assembly of the anode current collector 13and the anode 14 is placed. The separator 12 is filled with anelectrolyte that can transport ions between the anode and the cathode.The current collectors 10, 13 are used to collect the electrical energygenerated by the battery 15 and connect it to an outside device so thatthe outside device can be electrically powered and to carry electricalenergy to the battery during recharging.

Anodes of nonaqueous electrolyte secondary batteries can be made fromcomposite or monolithic anode materials. In composite anodes,particulate anode material is physically bound together with a binderforming a matrix of the particles and the binder. For example, anodescan be made from carbonaceous particles bound with a polymer binder.Monolithic anodes are anodes that are not made by the addition of aphysical binder material. For example, any method of creating of asilicon anode where the silicon molecules are interconnected without theaid of an external binding agent is a monolithic film. Examples ofmonolithic anode materials include monocrystalline silicon,polycrystalline silicon and amorphous silicon. Monolithic anodes canalso be formed by melting or sintering particles of anode material or byvacuum and chemical deposition.

During the charging process of the lithium-ion battery, the lithiumleaves the cathode and travels through the electrolyte in the separatoras a lithium ion and into the anode. During the discharge process, thelithium ion leaves the anode material, travels through the electrolytein the separator and passes through to the cathode. Elements likealuminum, silicon, germanium and tin react with lithium ions and areused in high-capacity anodes. Anode materials that react with lithiumhave active areas in which lithium can react and inactive areas in whichlithium cannot react. The ratio of the active to inactive area of theanode affects the efficiency of the battery.

In the reaction of lithium ions in a lithium-reactive material, there isa significant volume difference between the reacted and extractedstates; the reacted state of lithium-reactive anode materials occupiessignificantly more volume than the extracted state. Therefore, the anodechanges volume by a significant fraction during every charge-dischargecycle. In lithium-reactive anodes, cracks in the anode material areoften formed during the cycling volume change. With repeated cycling,these cracks can propagate and cause parts of the anode material toseparate from the anode. The separation of portions of the anode fromcycling is known as exfoliation. Exfoliation causes a decrease in theamount of active anode material that is electrically connected to thecurrent collector of the battery, thereby causing capacity loss.

Silicon anodes, which are excellent candidates for lithium-ion batteriesdue to silicon's high capacity for lithium, suffer from significantcapacity degradation due to cycling exfoliation. Reducing thecharged-to-discharged voltage window applied to a silicon anode in alithium-ion battery can stem the capacity loss due to cycling since theexpansion and contraction are a function of the state of charge. Butreducing the charged-to-discharged voltage window lowers the operatingcapacity of the battery. Also, silicon is a poor conductor and mustoften be formulated with conductive additives to function as an anodematerial. These conductive additives reduce the active to inactiveratio, thereby reducing the energy density of the battery. Conductiveadditives are typically materials like carbon black that are added tothe anode particles and mixed before binding the particles.

Another method to improve conductivity of an anode material is todeposit a layer of conductive material on an anode material. Methods fordeposition of conductive layers include vapor deposition,electro-deposition, and electroless deposition. When materials aredeposited using any of the above methodologies on resistive substrateslike silicon, the deposition across the anode is typically non-uniform.For example, in electroless plating and electroplating of metals such asnickel, the deposition rate on a nickel surface is significantly higherthan that on a dissimilar surface such as silicon. A deposition that hassuch significant kinetic variations on different materials causes thedeposition to have surface defects, pores, and areas of no deposition.In the case of a line of sight deposition processes like vacuumdeposition from a target, non-planar surfaces with areas that are not indirect line of sight get significantly less or no deposition therebyreducing thickness uniformity. In addition, these coatings may notadhere well since these coating methods have poor adhesion strength ofthe deposited metal to semiconductor material. The poor adhesionstrength, poor uniformity, and poor minimum thickness of these coatingsresult in poor cycle life, power, energy, and reliability.

SUMMARY OF THE INVENTION

The present invention relates to nonaqueous electrolyte secondarybatteries and durable anode materials and anodes for use in nonaqueouselectrolyte secondary batteries. The present invention also relates tomethods for producing these anode materials. In the present invention, alayer of metal-semiconductor alloy is formed on an anode material bycontacting a portion of the anode material with a solution containingions of the metal to be deposited and a dissolution component fordissolving a part of the semiconductor in the anode material. When theanode material is contacted with the solution, the dissolution componentdissolves a part of the semiconductor in the anode material therebyproviding electrons to reduce the metal ions and deposit the metal onthe anode material. After deposition, the anode material and metal areannealed to form a uniform metal-semiconductor alloy layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a cross section of a prior art lithium-ion battery; and

FIG. 2 illustrates the displacement process of an exemplary embodimentof the present invention.

FIG. 3 illustrates a semiconductor particle coated by ametal-semiconductor alloy layer.

FIG. 4 illustrates a semiconductor particle formed on a currentcollector and immersed in an electrolyte.

FIG. 5 illustrates an anode comprising pillars of semiconductorparticles with a metal-semiconductor alloy layer.

FIGS. 6A-6D illustrate a variety of anode structures.

DETAILED DESCRIPTION OF THE INVENTION

The inventors of the present invention have discovered that using adisplacement plating process to coat metal on a semiconductor-containinganode material followed by annealing results in thin and uniformmetal-semiconductor alloy coating for improved conductivity, withimproved weight fraction of active anode material, and reduced anodeexpansion without a substantial loss in efficiency.

The uniform metal-semiconductor alloy coating on an anode materialprovides significantly better electrical conductivity than the nativesemiconductor structure of the anode itself. For example, typicalsilicon powder has a resistivity of 1-100 Ω/cm; whereas a nickelsilicide layer of composition NiSi has a resistivity of 10-60 μΩ/cm.This provides an enormous advantage for use in a nonaqueous electrolytesecondary battery, such as a lithium-ion battery, since the coating alsoreduces the amount of conductive additive needed to make a workinganode. Since nickel silicide by itself lithiates reversibly, acombination of pure nickel silicide on silicon constitutes an anodematerial with both excellent electrical conductivity and excellentlithium cycling ability. The addition of fewer additives in theelectrode also improves the specific energy density of the electrodesince it has a lower amount of inactive material in the electrode.

The uniform metal-semiconductor alloy coating on an anode material alsoprovides uniformly high electrical conductivity thereby improving theability to lithiate the anode material surface uniformly, which in turncauses uniform expansion of the anode material and subsequently lesscapacity degradation due to exfoliation. Metal deposition andmetal-semiconductor alloy formation according to embodiments of thepresent invention are not dependant on the crystal orientation of theanode material.

For anodes in nonaqueous electrolyte secondary batteries, the presentmethod is superior to other methods of making metal-semiconductor alloycoating due to its selectivity, uniformity, and the improved electricalconductivity of the resultant material. These beneficial propertiesresult in anode materials for nonaqueous electrolyte secondary batteriesthat provide improved first cycle charge/discharge efficiency, longercycle life, more uniform charge/discharge, higher rate capability, andhigher specific energy density than currently used anode materials.

The present invention is directed to a method for forming an anodematerial having a metal-semiconductor alloy layer. The method comprisesobtaining an anode material comprising a semiconductor material;contacting a portion of the anode material with a metal ion solutioncomprising ions of a metal and a displacement solution comprising adissolution component for dissolving part of the semiconductor in theanode material, wherein the portion of the anode material contains thesemiconductor material; dissolving a part of the semiconductor materialfrom the portion of anode material; reducing the ions of the metal tothe metal by electrons provided by the dissolution of the semiconductormaterial; depositing the metal on the portion of the anode material; andannealing the portion of the anode material and the deposited metal toform a metal-semiconductor alloy layer.

In a method of the present invention, an anode material having a uniformmetal-semiconductor alloy layer is formed. A portion of an anodematerial that contains a semiconductor material is contacted with ametal ion solution containing ions of a metal and a displacementsolution containing a dissolution component. The metal ion solution andthe displacement solution are optionally premixed before contacting theportion of the anode material. The term “dissolution component” refersto a constituent that promotes dissolution of the semiconductormaterial. Dissolution components include fluoride, chloride, peroxide,hydroxide, permanganate, etc. Preferred dissolution components arefluoride and hydroxide. Most preferred dissolution component isfluoride. Some of the semiconductor material from the portion of anodematerial contacted with the dissolution component dissolves in thesolution. The dissolution of the semiconductor reduces ions of the metalin the displacement solution to the metal. The metal deposits out of thesolution onto the portion of the anode material. The portion of theanode material and the deposited metal are then annealed to convert thedeposited metal to metal-semiconductor alloy.

The anode material in this invention can be particulate in the form ofpowder with a variety of shapes such as spheroids, platelets, fibers,etc. The anode material in this invention can also be monolithic. Theanode material in this invention can further be in a matte form(collection of fibers.)

A specific example of nickel and silicon is illustrated in the followingembodiment. However, the processes of the present invention can be usedto deposit many other metals such as other base metals like copper andcobalt or noble metals like silver, gold, platinum, palladium, orrhodium. Preferably the metal ion solution contains ions of primarilyone metal, but it can contain ions of multiple metals. Semiconductormaterials useful for this invention include silicon, germanium, oralloys thereof such as silicon or germanium alloys with tin, zinc andmanganese. The semiconductor material can also be a compound like aIII-V compound such as aluminum antimonide (AlSb), indium antimonide(InSb), gallium arsenide (GaAs), and indium phosphide (InP); or a II-VIcompound such as cadmium telluride (CdTe), and cadmium-selenide (CdSe).

In the example of nickel deposition on a silicon-containing anodematerial, the nickel ions can be supplied to the metal ion solution byadding a nickel-containing salt, such as nickel sulfate or nickelchloride; the dissolution component can be a hydrolyzed fluoride ion,such as ammonium fluoride or hydrofluoric acid. The base material, inthis case silicon, dissolves in the solution providing the electrons forthe deposition of the nickel. Silicon at the surface of the anodematerial dissolves into solution. Nickel ions reduce on the surface ofthe silicon-containing anode material to deposit a metallic nickel filmthat is subsequently converted into nickel silicide by annealing. Sincethis process requires the dissolution of silicon for the deposition ofnickel, the deposition occurs only on the sites where the silicon candissolve. As a result, the film that is deposited on the silicon surfaceis extremely uniform, unlike in an electroless or electro-depositionprocess. Since it also involves the displacement of silicon atoms forthe deposition of a nickel atom, the adhesion of the metal coating onsilicon through this process is superior to an electroless depositionprocess.

Contact between a metal ion solution, a displacement solution and aportion of the anode material can be accomplished by various meansincluding partial and complete immersion, coating and spraying. FIG. 2is a schematic of a displacement process in which the anode material 21is immersed in a container 22 that contains solution 23, which is apremixed metal ion solution and displacement solution. As shown, theanode material 21 in FIG. 2 is in a particle form. In FIG. 2, the anodematerial is submerged in solution 23. However, only a portion of theanode material 21 may be contacted with solution 23. Solution 23contains a required amount of the salt of the metal to be depositedalong with an appropriate concentration of a dissolution component. Ingeneral, the solution contacting the anode material contains about0.01-1 M, preferably 0.02-0.5 M of metal ions; the solution furthercontains 0.02-8 M, preferably 0.5-5M of dissolution component. Thecontacting solution has a pH 6-11, preferably 8-10; and a temperature of40-98° C., preferably 50-98° C. Solution 23 can be kept within a settemperature range for a specified length of time in the container 22 forthe metal displacement to occur. When the desired thickness of the metalis achieved, the anode material is removed from the solution to berinsed, dried, and annealed.

The average thickness of metal deposited by this method on anodematerials can be between about 100 nanometers and 3 micrometers. Thinnercoatings do not provide the benefits of the invention. Coatings thickerthan 3 micrometers are possible but not cost effective.

Annealing is optionally performed in an inert atmosphere to form auniform metal-semiconductor alloy coating. For example, if the annealingatmosphere in the nickel-on-silicon example contains too much oxygen,the deposited nickel can be converted to nickel oxide instead of nickelsilicide in the annealing step. Annealing conditions for obtaining anickel silicide layer of good conductivity and good alloy uniformity aredisclosed in Waidmann et al., Microelectronic Engineering; Volume 83,Issue 11-12, Pages 2282-2286. In one example, annealing can be doneusing a rapid thermal anneal process at temperatures of about 500° C.Different annealing conditions provide silicides of varyingconductivities due to the formation of different alloy compositions. Theannealing conditions can be tailored for the resultant specificconductivities by changing the temperature and time of anneal.

In certain cases, such as when the annealing cycle needs to be short dueto process time constraints, the annealing conditions can be designedsuch that not all the deposited metal gets converted to ametal-semiconductor alloy. Excess metal can impede lithiation of themetal-semiconductor alloy and semiconductor material. In such ascenario, the excess metal that is not converted to metal-semiconductoralloy can be etched off using a solution that selectively etches themetal without etching the metal-semiconductor alloy. For example, asolution of sulfuric acid in hydrogen peroxide can selectively etchnickel without etching nickel silicide.

In one embodiment of the method of the present invention, the solutionthat contacts the anode material contains about 0.02-0.5 M Ni²⁺ asnickel sulfate, about 0.5-5 M fluoride as NH₄F, has a pH of about 8-10;and has a temperature of about at 50° C.-98° C.

In another embodiment of the method of the present invention, thesolution that contacts the anode material contains about 0.02-0.5 M Ni²⁺as nickel sulfate, about 0.5-5 M peroxide as H₂O₂; has a pH of about8-10; and has a temperature of about at 50° C.-98° C.

The method of the present invention is used to prepare an anode materialhaving a uniform metal-semiconductor alloy layer. Themetal-semiconductor alloy layer on an anode prepared by the methods ofthis claim is preferably a nickel silicide. Other metals may also beused on anodes prepared by the methods of this invention including otherbase metals like copper and cobalt or noble metals like silver, gold,platinum, palladium, or rhodium. Preferably, the thickness of themetal-semiconductor alloy on an anode prepared by the methods of thepresent invention is between about 100 nanometers and 3 micrometers.

A nonaqueous electrolyte secondary battery can be made using an anodematerial prepared by the methods of the present invention. A battery isformed using the anodes of the present invention by combining them withcathodes and electrolytes in planar or three dimensional structures asknown in the art. See, e.g., Long et. al., Three-Dimensional BatteryArchitectures, Chemical Reviews, 2004, 104, 4463-4492. The nonaqueouselectrolyte secondary battery of the present invention can be alithium-ion battery, a sodium-ion battery, a potassium-ion battery, oranother type of nonaqueous electrolyte secondary battery. The nonaqueouselectrolyte secondary battery comprises an anode formed from an anodematerial having a metal-semiconductor alloy layer, a cathode, and anonaqueous electrolyte.

In another embodiment, the present invention is directed to a method forforming an anode having a metal-semiconductor alloy layer comprising thesteps of: obtaining a particulate anode material comprising asemiconductor material; contacting the particulate anode material withthe a metal ion solution comprising metal ions and a displacementsolution comprising a dissolution component for dissolving part of thesemiconductor material in the particulate anode material; dissolving apart of the semiconductor material from the particulate anode material;reducing the ions of the metal to the metal by electrons provided by thedissolution of the semiconductor; depositing the metal on theparticulate anode material; shaping the particulate anode material; andsintering the particulate anode material to agglomerate the particulateanode material. The semiconductor material, the metal, and thedissolution component are the same as those described already in theapplication. The method optionally comprises a step of annealing theparticulate anode material and the deposited metal to form ametal-semiconductor alloy layer prior to shaping the particulate anodematerial.

In a further embodiment, the present invention is directed to a methodfor forming an anode having a metal-semiconductor alloy layer comprisingthe steps of: obtaining a particulate anode material comprising asemiconductor material; shaping the particulate anode material;contacting the particulate anode material with the a metal ion solutioncomprising metal ions and a displacement solution comprising adissolution component for dissolving part of the semiconductor materialin the particulate anode material; dissolving a part of thesemiconductor material from the particulate anode material; reducing theions of the metal to the metal by electrons provided by the dissolutionof the semiconductor; depositing the metal on the particulate anodematerial; and sintering the particulate anode material to agglomeratethe particulate anode material. The semiconductor material, the metal,and the dissolution component are the same as those described already inthe application.

In the present invention, semiconductor-containing anode particles arecoated with a metal or metal-semiconductor alloy then shaped andsintered to form anodes. Anodes formed by this process have the benefitsof the metal-semiconductor alloy layer described above and havesufficient porosity create increased surface area for reaction with ionsfrom an electrolyte in a nonaqueous electrolyte secondary battery. Theincreased contact area with the electrolyte allows a very high weightfraction of active semiconductor anode material. Sintering of the coatedparticles of semiconductor anode material comprises heating the coatedmaterial well below melting point of the semiconductor material untilthe particles adhere to each other. Sintering of the particles may bedone after the coated particles are annealed to for ametal-semiconductor alloy or the annealing may be done simultaneouslywith the sintering step.

FIG. 3 is an illustration of a semiconductor particle 30 coated in ametal-semiconductor alloy layer 31. FIG. 4 illustrates a layer 41 ofsintered semiconductor particles formed on a current collector 40 andimmersed in an electrolyte 43 containing ions as part of a battery.Since the metal-semiconductor alloy coating 44 on the semiconductorparticles 45 is conductive, the sintered particles are electricallyconnected to each other and to the current collector. This allows foruniform charge distribution across the layer 41 of sinteredsemiconductor particles. Since the layer 41 of sintered semiconductorparticles is porous, the layer 41 has increased surface area for theelectrolyte 43 to contact.

FIG. 5 is an illustration of an anode that uses pillars 51 of sinteredsemiconductor particles with a metal-semiconductor layer. The pillars 51are formed on a current collector 50. FIGS. 6A through 6D show that avariety of other anode structures 60 can be formed from sinteredsemiconductor particles with a metal-semiconductor alloy layer. In FIGS.6A to 6D, a cathode structure 61 that can be used with each of the anodestructures 60 in a battery is shown.

The particulate anode material having a metal-semiconductor alloy layercan be shaped using a mold, or coated onto a structure. Coating can bedone using conventional methods such as reverse roll, or moresophisticated techniques like electrophoretic deposition.

Preferably, the metal-semiconductor layer on the semiconductor anodematerial is thick enough to provide adhesion and cohesion of theparticles, but thin enough so as not to dominate the electrochemicalbehavior of the electrode. In one embodiment, the metal-semiconductoralloy coating is about 0.1% to 5% of the total particle volume, whilethe particles can be about 0.001 microns to 100 microns in diameter. Theparticles can have a variety of shapes including platelets and rods.Since the particle shapes may be irregular, the diameter of theparticles is defined as the longest distance from one point of theparticle to another point of the particle.

One embodiment of this invention includes a nickel foil or mesh coatedwith sintered silicon particles.

A nonaqueous electrolyte secondary battery can be made using an anodeprepared by the methods of the present invention. The nonaqueouselectrolyte secondary battery of the present invention can be alithium-ion battery, a sodium-ion battery, a potassium-ion battery, oranother type of nonaqueous electrolyte secondary battery. The nonaqueouselectrolyte secondary battery comprises an anode having ametal-semiconductor alloy layer, a cathode, and a nonaqueouselectrolyte.

The following examples further illustrate the present invention. Theseexamples are intended merely to be illustrative of the present inventionand are not to be construed as being limiting.

EXAMPLES Example 1 Immersion Nickel Deposition on Particulate AnodeMaterial

A sample of 2 grams of silicon particulates in powder form (−325 mesh)was immersed for 30 seconds in 50 milliliters of a solution containing0.1 M NiSO₄.6H₂O and 5M NH₄F. The pH of the solution was maintained at8.5 and the operating temperature was 85° C. Deposition was done withthe powder on top of a filter paper assembled in a Buchner funnel.Vigorous bubbles were observed during deposition indicating the nickeldisplacement reaction. The solution was drained out through theapplication of vacuum in the Buchner funnel. The sample was rinsed withDI water for 10 minutes to remove trace salt contamination. The powderwas harvested and dried at 80° C. in air for 12 hours. Subsequently, thepowder was annealed for 2 hours (including heat and cool time) to amaximum temperature of 550° C. in a H₂/N₂ atmosphere to form thesilicide.

The resulting anode material was reversibly cycled upwards of 1200 mAh/gof silicon equivalent for 100 cycles at an average coulombic efficiencyof 99.8% for the 100 cycles. This was in contrast to a silicon powderalone which degraded to less than 330 mAh/g capacity of silicon by the10th charge-discharge cycle.

Example 2 Immersion Nickel Deposition on Particulate Anode Material

A sample of 2 grams of silicon particulates in powder form (−325 mesh)was immersed for 30 seconds in 50 milliliters of a solution containing0.1 M NiSO₄.6H₂O and 5M NH₄F. The pH of the solution was maintained at8.5 and the operating temperature was 85° C. Deposition was done withthe powder on top of a filter paper assembled in a Buchner funnel.Vigorous bubbles were observed during deposition indicating the nickeldisplacement reaction. The solution was drained out through theapplication of vacuum in the Buchner funnel. The sample was rinsed withDI water for 10 minutes to remove trace salt contamination. The powderwas harvested and dried at 80° C. in air for 12 hours. Subsequently, thepowder was annealed for 2 hours (including heat and cool time) to amaximum temperature of 550° C. in a H₂/N₂ atmosphere to form thesilicide.

The powder prepared was immersed in a solution of 10 ml H₂SO₄+40milliliters 3% H₂O₂ at 70° C. for 3 minutes to remove any excess nickeland to leave behind the silicide.

Example 3 Sintering Mesh of Silicon Particles Coated in Nickel Silicide

Powder consisting of nickel silicide coated particles prepared accordingto Example 2 are dispersed in an aqueous solution containingcarboxymethylcellulose and coated onto a nickel mesh. The coated mesh isdried to remove water and then heated to 1000° C. in an argon atmosphereto sinter the nickel silicide coated particles to each other and to thenickel mesh. The resultant sintered electrode is used as an anode in alithium-ion battery.

Example 4 Sintering Mesh of Silicon Particles Coated in Nickel

A sample of 2 grams of silicon particulates in powder form (−325 mesh)is immersed for 30 seconds in 50 milliliters of a solution containing0.1 M NiSO₄.6H₂O and 5M NH₄F. The pH of the solution is maintained at8.5 and the operating temperature is 85° C. Deposition is done with thepowder on top of a filter paper assembled in a Buchner funnel. Vigorousbubbles are observed during deposition indicating the nickeldisplacement reaction. The solution is drained out through theapplication of vacuum in the Buchner funnel. The sample is rinsed withDI water for 10 minutes to remove trace salt contamination. The powderis dispersed in an aqueous solution containing carboxymethylcelluloseand coated onto a nickel mesh. The coated mesh is dried to remove waterand then heated to 1000° C. in an argon atmosphere to simultaneouslyform a nickel silicide coating on the silicon particles and sinter thenickel silicide coated particles to each other and to the nickel mesh.The resultant sintered electrode is used as an anode in a lithium-ionbattery.

Example 5 Sintering Mesh Coated with Silicon Particles and Then Coatedwith Nickel

First silicon particles are dispersed in an aqueous solution containingcarboxymethylcellulose and coated onto a nickel mesh. The resultant meshwith silicon particles are coated with nickel using an immersiondisplacement coating process. The coated mesh is dried to remove waterand then heated to 1000° C. in an argon atmosphere to simultaneouslyform a nickel silicide coating on the silicon particles and sinter thenickel silicide coated particles to each other and to the nickel mesh.The resultant sintered electrode is used as an anode in a non-aqueouselectrolyte battery.

Although the invention has been described with reference to thepresently preferred embodiments, it should be understood that variousmodifications could be made without departing from the scope of theinvention.

What is claimed is:
 1. A secondary battery comprising an anode, acathode and a non aqueous electrolyte, the anode comprising a porousagglomerated mass of a sintered particulate material, wherein theparticulate material comprises a semiconductor material core and ametal-semiconductor alloy layer thereon and has a diameter of about0.001 micrometers to 100 micrometers, the volume of themetal-semiconductor alloy layer is about 0.1% to 5% of the totalparticle volume; and wherein particles within the agglomerated mass areadhered together by the metal-semiconductor alloy layer.
 2. Thesecondary battery of claim 1 wherein the semiconductor materialcomprises silicon or germanium.
 3. The secondary battery of claim 2wherein the metal of the metal-semiconductor alloy is nickel, copper,cobalt, silver, gold, platinum, palladium or rhodium.
 4. The secondarybattery of claim 2 wherein the metal of the metal-semiconductor alloy isnickel.
 5. The secondary battery of claim 1 wherein the metal of themetal-semiconductor alloy is nickel, copper, cobalt, silver, gold,platinum, palladium or rhodium.
 6. The secondary battery of claim 1wherein the metal of the metal-semiconductor alloy is nickel.
 7. Thesecondary battery of claim 1 the metal-semiconductor alloy layer has athickness of about 100 nanometers to 3 micrometers.
 8. The secondarybattery of claim 1 wherein the secondary battery comprises an anodecurrent collector and the anode is formed on the anode currentcollector.
 9. The secondary battery of claim 1 wherein porous mass of asintered particulate material is in the shape of a pillar.
 10. Thesecondary battery of claim 1 wherein the secondary battery is a lithiumion battery.
 11. The secondary battery of claim 10 wherein thesemiconductor material comprises silicon or germanium.
 12. The secondarybattery of claim 11 wherein the metal of the metal-semiconductor alloyis nickel, copper, cobalt, silver, gold, platinum, palladium or rhodium.13. The secondary battery of claim 11 wherein the metal of themetal-semiconductor alloy is nickel.
 14. The secondary battery of claim10 wherein the metal of the metal-semiconductor alloy is nickel, copper,cobalt, silver, gold, platinum, palladium or rhodium.
 15. The secondarybattery of claim 10 wherein the metal of the metal-semiconductor alloyis nickel.
 16. The secondary battery of claim 10 the metal-semiconductoralloy layer has a thickness of about 100 nanometers to 3 micrometers.17. The secondary battery of claim 10 wherein the secondary batterycomprises an anode current collector and the anode is formed on theanode current collector.
 18. The secondary battery of claim 10 whereinporous mass of a sintered particulate material is in the shape of apillar.
 19. The secondary battery of claim 10 wherein the semiconductormaterial comprises silicon, the metal-semiconductor alloy is nickelsilicide, and the metal-semiconductor alloy layer has a thickness ofabout 100 nanometers to 3 micrometers.
 20. The secondary battery ofclaim 19 wherein porous mass of a sintered particulate material is inthe shape of a pillar.
 21. The secondary batter of claim 1, wherein themetal-semiconductor alloy layer provides both adhesion and cohesion ofthe particles in the porous agglomerated mass.